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Thread: 308 ak

  1. #131
    Gunco Member bert01's Avatar
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    sorry for the long post just trying to get it easy to read, got some of the info from www.thegunzone.com/30cal.html trying to do everything on the safe side hence the max proof pressures for the 308 stuff and the bolt head diameter instead of the true case head diameter

    i got some good solid works 3D models of a romy trunnion today trying to run the force application on it as we speak (test how the lugs will hold up under different pressures applied from the bolt thrust)

    not having much luck the software im using doesnt allow for heat treated steel so even the opperating pressures of the 7.62 x 39 arent giving safe results in the solid model stuff

    ill keep trying and let you know what happens


    Bolt thrust= area x psi

    Area = 3.146 x ( (case head diameter / 2)^2)

    Above is from http://www.riflebarrels.com/articles...g_strength.htm


    7.62 x 51 NATO

    "Proof" pressure = 67,500 psi
    Bolt head diameter = .475

    3.146 x ((.475 / 2)^2) = .1772

    67,500 x .1772 = +/- 12,000

    7.62 x 51 NATO = +/- 12,000 lbs bolt thrust max

    308 Winchester

    "Proof" pressure = 83,000 psi
    Bolt head diameter = .475

    3.146 x ((.475 / 2)^2) = .1772

    83,000 x .1772 = +/- 14,800

    308 Winchester = +/- 14,800 lbs bolt thrust max

    7.62 x 39

    Max "reload" pressure = 45,000 psi
    bolt head diameter = .458

    3.146 x ((.458 / 2)^2) = .1647

    45,000 x .1647 = +/- 7,420

    7.62 x 39 = +/- 7,420 lbs bolt thrust

    6.5 Grendel

    Case head diameter = .445

  2. #132
    Gunco Member bert01's Avatar
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    okay putting the force application stuff off till tomorrow

    but i was doing some figuring with the formula for bolt shear strength from the lilja website. i used the small lug on a romy bolt.
    the height i used was .27, length .423, 2 lugs, and 100,000 psi yield strength for hardened 1050

    .27 x .423 x 2 x 100,000 = 22,842 then divide by a safety factor of 2 and you get 11,421 psi of bolt thrust before shear occurs

    the 100,000 yield strength nums are for 1050 hardened to rc 30, i got 1050 from a post on another site, but as for the rc number im not sure, the psi num drops pretty sharp as hardness goes down

    C:\Documents and Settings\ba\Desktop\Ruger Investment Casting - Steel.htm

    BG can you get the measurements from a m70 bolt?

  3. #133
    rbthntr64's Avatar
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    I will compare the yugo and the VEPR. 1st dim. .405/.537 2nd. .621/.722 Bolt face .452/.483 Interesting difference is the bottom front .424/.422 The Bulgy 5.45 bolt is .333. The VEPR is a small stem bolt with a spring loaded firing pin. Lightning cuts are the same from the 5.45 to the VEPR. Bolt heigth from the 5.45 to the VEPR .839/.926. The yugo is .917. Bolt length yugo 3.335 vepr 3.438 bul 3.439 Trunion lugs are the same as the yugo on the VEPR.
    Freedom is not free. Some will perish to preserve it for the many. Just as our Forefathers did before us, we must take up the battle and not waver. Victory is our only option.

  4. #134
    Gunco Regular Gunter's Avatar
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    Bert, I think there is a mistake in your figures. LS=(LxLLxNLxYS)/2

    L is the length of the arc segment not the height of the lug. Finding the radius of an AK bolt is a little tough. I'll measure a trunnion in a while and see if we can get a radius.

  5. #135
    Gunco Member bert01's Avatar
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    if i understand your deminsions correctly, the height of the lug is .405, length .621 for the yugo m70

    so using the same yield strength and 2 lugs

    .405 x .621 x 2 x 100,000 = 50,031 divide by safety factor of 2 = 25,150.5 lbs of thrust before shear occurs. this is well under even the calculated bolt thrust with proof loads from above (14,800 lbs of thrust)

    does this sound right?

  6. #136
    Gunco Member DaveGP's Avatar
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    As an aside - the Galil in 308 uses what appears to be a garden-variety AK bolt...maybe we are getting a bit carried away here?

  7. #137
    Gunco Member bert01's Avatar
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    you are right about the height vs radius, but in this case the height of the lug would be only slightly smaller than the arc segment. so its a lot easier to obtain and if any error occors because of it it is on the side of safety

  8. #138
    Gunco Member bert01's Avatar
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    plus i think you only need the arc segment if force is applied in an arc, meaning that the trunnion and bolt contact edges are arced. right?

  9. #139
    rbthntr64's Avatar
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    the length is .405 heigth is .160 for the short lug the other is .621 and .177 respectively
    Freedom is not free. Some will perish to preserve it for the many. Just as our Forefathers did before us, we must take up the battle and not waver. Victory is our only option.

  10. #140
    rbthntr64's Avatar
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    There is nothing in the ROBARMS manual resticting use of any .308 ammo. Guys these VEPR rifles have been thoroughly tested in Russia. If there was an issue of strength, ROBARMS would definitely identify it for liability purposes. I think as long as you use a bulged trunion in your build there shouldn't be a problem.
    Freedom is not free. Some will perish to preserve it for the many. Just as our Forefathers did before us, we must take up the battle and not waver. Victory is our only option.

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